Replication and availability in decentralised online social networks
SubjectsG420 Networks and Communications
online social networks
MetadataShow full item record
AbstractDuring the last few years’ online social networks (OSNs) have become increasingly popular among all age groups and professions but this has raised a number of issues around users’ privacy and security. To address these issues a number of attempts have been made in the literature to create the next generation of OSNs built on decentralised architectures. Maintaining high data availability in decentralised OSNs is a challenging task as users themselves are responsible for keeping their profiles available either by staying online for longer periods of time or by choosing trusted peers that can keep their data available on their behalf. The major findings of this research include algorithmically determining the users’ availability and the minimum number of replicas required to achieve the same availability as all mirror nodes combined. The thesis also investigates how the users’ availability, replication degree and the update propagation delay changes as we alter the number of mirror nodes their online patterns, number of sessions and session duration. We found as we increase the number of mirror nodes the availability increases and becomes stable after a certain point which may vary from node to node as it directly depends on the node’s number of mirror nodes and their online patterns. Moreover, we also found the minimum number of replicas required to achieve the same availability as all mirror nodes combined and update propagation delay directly depends on mirror nodes’ number of sessions and session duration. Furthermore, we also found as we increase the number of sessions with reduced session lengths the update propagation delay between the mirror nodes starts to decrease. Thus resulting in spreading the updates faster as compared to mirror nodes with fewer sessions but of longer durations.
CitationHassan, A. (2017) 'Replication and availability in decentralised online social networks'. MPhil thesis. University of Bedfordshire.
PublisherUniversity of Bedfordshire
TypeThesis or dissertation
DescriptionA thesis submitted to the University of Bedfordshire in partial fulfilment of the requirements for the degree of Master of Philosophy
The following license files are associated with this item:
- Creative Commons
Except where otherwise noted, this item's license is described as http://creativecommons.org/licenses/by-nc-nd/4.0/
Showing items related by title, author, creator and subject.
Application of optimization methods for resource allocation in cognitive radio-supported vehicular networksEze, Joy Chinedu (University of BedfordshireUniversity of Bedfordshire, 2021-07)The highly anticipated era of vehicular communication networks which is also an integral aspect of Intelligent Transportation Systems (ITS) will undeniably improve transport safety and significantly reduce road accidents. To promote the communication of mobile vehicles, US FCC officially allocated a meagre 75 MHz spectrum in the 5.9 GHz band to enable vehicular communication. Cognitive Radio Networks (CRNs) are adaptive, intelligent and reconfigurable wireless communications systems with CR technologies capable of learning from their surroundings and deciding their operations based on the learning. The application of CR technology to vehicular networks in order to increase the spectrum resource opportunities is studied in this research. Applying CR technology to vehicular networks is crucial especially when the officially allocated 75 MHz spectrum in 5.9 GHz band is not enough due to high demands as a result of increasing number of connected vehicles as already foreseen in the near era of Internet of vehicles (IoVs), which is also known as vehicular ad hoc networks (VANETs). We proposed a novel CR Assisted Vehicular NETwork (CRAVNET) framework which empowers CR assisted vehicles to make opportunistic usage of licensed spectrum bands on the highways and developed a novel co-operative three-state spectrum sensing and allocation solution which makes CR vehicular SUs aware of additional spectrum resources opportunities on their current and future positions. Furthermore, a novel Adaptive CR Enabled Vehicular NETwork (ACRAVNET) framework is proposed to ensure high spectrum sensing efficiency and provide quality of service (QoS) support. To avoid heavy overhead usually incurred during spectrum sensing, we developed a novel CR adaptive spectrum sensing (CRASS) scheme that can reduce the spectrum sensing cost and improve sensing performance effectively. We also applied the concept of Nash Bargaining Solution (NBS) to guarantee fairness in spectral resources allocation and proposed a generalized non-symmetric NBS (GNNBS) to perform a non-symmetric cognitive inter-cell spectrum allocation in the proposed ACRAVNET framework. Both the simulation and theoretical analysis have demonstrated that our solution can significantly improve the performance of a cooperative spectrum sensing and sharing schemes and provide vehicles with additional spectrum opportunities with zero interference against the PUs activities. Additionally, the problem of joint optimal subcarrier and transmission power allocation with QoS support for enhanced packet transmission over a cognitive radio-enabled IoVs network system is also considered in this research study. To tackle the problem, a novel Symmetric Nash bargaining solution (SNBS) based wireless radio resource scheduling scheme in orthogonal frequency division multiple access (OFDMA) CR enabled IoVs network systems is proposed. The objective of the optimization model applied in this study is to maximize the overall system throughput of the CR enabled IoVs system without harmful interference to transmissions of the shared channels’ licensed owners (or primary users (PUs)), guarantee the proportional fairness and minimum data-rate requirement of each CR vehicular secondary user (CRV-SU) and efficient transmission power allocation amongst CRV-SUs. To avoid the iterative processes associated with searching the optimal solution numerically through iterative programming methods, this study developed a low-complexity algorithm. Theoretical analysis and simulation results demonstrate that under similar conditions, the proposed solutions outperform the reference scheduler schemes.
Spatial diversity for wireless LANsBrito, Rodrigo; Allen, Ben; Dohler, Mischa; Aghvami, A.Hamid; University of Bristol (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2004-05)Wireless local area networks (W-LAN) are widely used as a means of providing broadband access for high-speed wireless data services. The maximization of the system performance independent of the transceiver technology and the operating environment is of utmost importance to the hotspot system designer. This paper reports on the performance of single input and multiple output (SIMO) W-LAN systems and shows that a circular array topology located at the access point provides the best performance improvement compared to other candidate technologies when operating in an indoor office environment.
Cross-validation based man-in-the-middle attack protectionCui, Xiaofei (University of Bedfordshire, 2017-03)In recent years, computer network has widely used in almost all areas of our social life. It has been profoundly changing the way of our living. However, various network attacks have become an increasingly problem at the same time. In local area networks, Man-in-the-Middle attack, as one kind of ARP attack, is the most common attack. This research implemented a cross-validation based Man-in-the-Middle attack protection method (CVP). This approach enables a host to check whether another host that responds the initialising host with an ARP reply packet is genuine. It then allows the ARP cache table of the initialising hosts to be updated with the MAC address and IP address pairs of the genuine host and to place the MAC address of inauthentic hosts into a blacklist. This research introduced ARP and ICMP firstly, including the structure of ARP and ICMP packets, and their workflows. Secondly, this research discussed the types of ARP attacks and the existing ARP attacks protection methods, including their principles, applicable environment, advantages and disadvantages. Then, this research proposed and implemented a cross-validation based Man-in-the-Middle attack protection method. Simulations and experiments were performed to examine the effect of CVP method. The results show the effectiveness of the proposed cross-validation based method in protecting network from Man-in-the-Middle attack. Compared with the existing Man-in-the-Middle attack protection methods, CVP requires no extra devices and administration, leading to more secure local area networks and low cost. It also has made a “tabu” to attackers. That is, it places the MAC address of attackers into a blacklist. So they will be identified immediately if they try to attack the network again.